{"id":"9cf30bca-14a6-4327-95a2-eafd5103d89c","shortId":"L27KCT","kind":"x402","title":"x402-gated premium API access on Base, pay $0.02 per request in USDC — no API keys required.","tagline":"x402-gated premium API access on Base, pay $0.02 per request in USDC — no API keys required.","description":"lowpaymentfee.com offers a suite of pay-per-call API endpoints gated by the x402 protocol on the Base network. The specific endpoint `/api/v1/cards/6` is listed as \"Premium API Access\" and returns a 402 challenge requesting payment in USDC (contract 0x8335…2913 on Base). The maximum amount required per call is 20,000 base units of USDC (6 decimals), which equals $0.02 USD. Payment is made via the x402 exact scheme with no API keys, subscriptions, or rate limits advertised.\n\nThe broader lowpaymentfee.com platform advertises endpoints across four categories: Data & Analytics (metrics, reports, data export, insights), AI & Machine Learning (sentiment analysis, text summarization, classification, embeddings), Finance & Web3 (price feeds, exchange rates, token quotes, gas estimates), and Infrastructure (geocoding, validation, conversion, generation). All endpoints are listed at the same $0.02/request price point. However, the `/api/v1/cards/6` endpoint does not clearly map to any of these named categories, and its specific functionality beyond \"Premium API Access\" is undocumented.\n\nDocumentation is extremely sparse — the /docs, /api, /pricing, and /README pages all render only a \"Connect wallet\" prompt with no further content. There is no OpenAPI spec, no request/response schema, and no usage examples available. The endpoint is confirmed live (402 challenge captured), but without documentation it is unclear what data or service this specific endpoint returns.","tags":[],"capabilities":["x402-payment","usdc-base","pay-per-request","no-api-key","json-response"],"categories":["api-gateway","misc"],"synonyms":["x402 API","pay-per-call API","USDC micropayment API","Base network API","lowpaymentfee","premium API access","crypto-gated endpoint"],"warnings":["No documentation available — /docs, /api, /pricing, and /README pages all show only 'Connect wallet' with no content.","The specific function of /api/v1/cards/6 ('Premium API Access') is completely undocumented; it does not map to any named endpoint on the landing page.","No request body schema or response schema is provided; integrators cannot know what to send or what to expect back.","No OpenAPI or machine-readable spec is available."],"endpointUrl":"https://lowpaymentfee.com/api/v1/cards/6","protocol":"x402","transport":"http","auth":{"type":"x402","details":[{"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","extra":{"name":"USD Coin","version":"2"},"payTo":"0x1A2B13E97f5F837C8F9FA1F95a1484B7C70d85F3","scheme":"exact","network":"base","mimeType":"application/json","resource":"https://lowpaymentfee.com/api/v1/cards/6","description":"Premium API Access","outputSchema":{"input":{"type":"http","method":"GET","discoverable":true}},"maxAmountRequired":"20000","maxTimeoutSeconds":300}]},"qualityScore":"0.300","qualityRationale":"The endpoint is confirmed live with a valid 402 challenge, but there is zero documentation on what it actually returns. No OpenAPI spec, no request/response schema, no examples. The endpoint name 'cards/6' and description 'Premium API Access' are opaque. Score reflects a live but essentially undocumented 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'/api/v1/cards/6':60,171 '/docs':198 '/pricing':200 '/readme':202 '/request':166 '0.02':10,28,98,165 '000':89 '0x8335':77 '20':88 '2913':78 '402':70,233 '6':94 'Base network API' 'USDC micropayment API' 'access':6,24,66,190 'across':123 'advertis':116,121 'ai':133 'amount':83 'analysi':137 'analyt':127 'api':5,16,23,34,46,65,110,189 'avail':227 'base':8,26,55,80,90 'beyond':187 'broader':118 'call':45,86 'captur':235 'categori':125,182 'challeng':71,234 'classif':140 'clear':175 'confirm':231 'connect':208 'content':214 'contract':76 'convers':156 'crypto-gated endpoint' 'data':126,130,243 'decim':95 'document':193,238 'embed':141 'endpoint':47,59,122,159,172,229,248 'equal':97 'estim':151 'exact':106 'exampl':226 'exchang':146 'export':131 'extrem':195 'feed':145 'financ':142 'four':124 'function':186 'gas':150 'gate':3,21,48 'generat':157 'geocod':154 'howev':169 'infrastructur':153 'insight':132 'json-response' 'key':17,35,111 'learn':135 'limit':115 'list':62,161 'live':232 'lowpaymentfee' 'lowpaymentfee.com':37,119 'machin':134 'made':102 'map':176 'maximum':82 'metric':128 'name':181 'network':56 'no-api-key' 'offer':38 'openapi':218 'page':203 'pay':9,27,43 'pay-per-cal':42 'pay-per-call API' 'pay-per-request' 'payment':73,100 'per':11,29,44,85 'platform':120 'point':168 'premium':4,22,64,188 'premium API access' 'price':144,167 'prompt':210 'protocol':52 'quot':149 'rate':114,147 'render':205 'report':129 'request':12,30,72 'request/response':221 'requir':18,36,84 'return':68,249 'schema':222 'scheme':107 'sentiment':136 'servic':245 'spars':196 'spec':219 'specif':58,185,247 'subscript':112 'suit':40 'summar':139 'text':138 'token':148 'unclear':241 'undocu':192 'unit':91 'usag':225 'usd':99 'usdc':14,32,75,93 'usdc-base' 'valid':155 'via':103 'wallet':209 'web3':143 'without':237 'x402':2,20,51,105 'x402 API' 'x402-gated':1,19 'x402-payment'","prices":[{"id":"38a91ef2-e838-4333-bf7c-32d8a8a0280e","listingId":"9cf30bca-14a6-4327-95a2-eafd5103d89c","amountUsd":null,"unit":"per_call","nativeCurrency":"USD COIN","nativeAmount":"20000","chain":"base","payTo":"0x1A2B13E97f5F837C8F9FA1F95a1484B7C70d85F3","paymentMethod":"x402-usd coin","isPrimary":true,"details":{"scheme":"exact","mime_type":"application/json","accepts_all":[{"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","extra":{"name":"USD Coin","version":"2"},"payTo":"0x1A2B13E97f5F837C8F9FA1F95a1484B7C70d85F3","scheme":"exact","network":"base","mimeType":"application/json","resource":"https://lowpaymentfee.com/api/v1/cards/6","description":"Premium API Access","outputSchema":{"input":{"type":"http","method":"GET","discoverable":true}},"maxAmountRequired":"20000","maxTimeoutSeconds":300}],"asset_contract":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","max_timeout_seconds":300},"createdAt":"2026-04-18T18:43:50.952Z"}],"sources":[{"listingId":"9cf30bca-14a6-4327-95a2-eafd5103d89c","source":"x402_bazaar","sourceId":"https://lowpaymentfee.com/api/v1/cards/6","sourceUrl":"https://api.cdp.coinbase.com/platform/v2/x402/discovery/resources","isPrimary":true,"firstSeenAt":"2026-04-18T18:43:50.952Z","lastSeenAt":"2026-04-22T10:01:40.783Z"}],"details":{"listingId":"9cf30bca-14a6-4327-95a2-eafd5103d89c","quickStartSnippet":"# The endpoint requires an x402 payment header (USDC on Base).\n# 1. Send POST to get the 402 challenge:\ncurl -X POST https://lowpaymentfee.com/api/v1/cards/6\n# 2. Parse the 402 JSON, construct an x402 payment proof for 20000 base units ($0.02 USDC),\n#    then resend with the X-PAYMENT header:\ncurl -X POST https://lowpaymentfee.com/api/v1/cards/6 \\\n  -H \"X-PAYMENT: <signed-payment-payload>\"","exampleRequest":null,"exampleResponse":null,"schema":{"input":{"type":"http","method":"GET","discoverable":true}},"openapiUrl":null,"agentsTxtUrl":null,"citations":[{"claim":"The endpoint returns a 402 challenge requesting 20000 base units of USDC on Base (asset 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913).","source_url":"https://lowpaymentfee.com/api/v1/cards/6"},{"claim":"All listed endpoints are priced at $0.02 per request with no API keys, no rate limits, and instant access on Base network.","source_url":"https://lowpaymentfee.com"},{"claim":"The platform offers endpoints in Data & Analytics, AI & Machine Learning, Finance & Web3, and Infrastructure categories.","source_url":"https://lowpaymentfee.com"},{"claim":"Documentation pages (/docs, /api, /pricing, /README) render only a 'Connect wallet' prompt with no further content.","source_url":"https://lowpaymentfee.com/docs"}],"useCases":["Accessing premium data or services with per-request USDC micropayments on Base","Agent-driven API consumption without pre-registration or API key management","Programmatic pay-as-you-go access to undocumented premium content"],"bestFor":["Developers wanting zero-signup, pay-per-call API access","AI agents with x402 payment capability on Base","Users who prefer crypto micropayments over subscription billing"],"notFor":["Users who need detailed API documentation or response schemas before integrating","Anyone without a Base-compatible USDC wallet","High-volume consumers who need bulk pricing or rate guarantees"],"kindDetails":{"x402_version":1,"resource_type":"http","bazaar_last_updated":"2026-02-17T23:14:26.135Z"},"updatedAt":"2026-04-22T10:01:40.783Z"}}